Conventionally, a fin for a heat exchanger has multiple louvers on a surface of the fin, and the louvers are arranged in an air flow direction. The louvers are provided by cutting the fin and raising the cut part of the fin. A variety of technologies have been proposed for, improvement of a heat exchange capacity of the fin by changing shapes of the louvers, such as a length and an inclined angle of the cut part of the fin (e.g., refer to Patent Document 1 (JP 4690605 B2), Patent Document 2 (U.S. Pat. No. 5,730,214 A), Patent Document 3 (JP 2005-003350 A corresponding to US 2007/0051502A1) and Patent Document 4 (JP 5-045474 U)).
A fin for a heat exchanger described in Patent Document 1 includes a changing part provided at a center part of the fin in an air flow direction, and the air flow direction is changed at the changing part. The fin has downstream louvers located downstream of the changing part, and upstream louvers located upstream of the changing part in the air flow direction. The downstream louvers are inclined from a surface of the fin at an angle smaller than that of the upstream louvers.
A fin for a heat exchanger described in Patent Document 2 includes a changing part, upstream louvers and downstream louvers, similarly to Patent Document 1. The upstream louvers are arranged such that inclined angles of thereof are gradually increased in an air flow direction in a steady pattern, and the downstream louvers are arranged such that inclined angles thereof are gradually decreased in the air flow direction in a steady pattern.
In a heat exchanger described in Patent Document 3, long louvers and short louvers are alternatively arranged to improve an efficiency of heat exchange of a fin. In a heat exchanger described in Patent Document 4, a most downstream louver of multiple louvers in an air flow direction has a length longer than that of the other louvers, or is separated from a louver adjacent to the most downstream louver by a distance longer than distances between other two of the multiple louvers.
When a louver pitch is decreased so that the number of louvers is increased in a fin, a heat transfer efficiency of the fin can be increased due to edge effects of the louvers, and a heat exchange capacity of the fin can be thereby increased.
However, when the louver pitch is decreased so that the number of louvers is increased, an airflow resistance of the fin may be increased due to decrease of a total area of louver passages provided between two louvers adjacent to each other. When a heat exchanger provided with the fin is combined with a blower fan that blows air to the heat exchanger, a flow rate of air flowing through the louver passages may decrease, and the heat exchange capacity of the fin may decrease as a result. In other word, even when only the louver pitch made to be short in the fin having multiple louvers, the heat exchange capacity may not be increased.